1. Field of the Invention
The present invention relates to a cutting method and a cutting apparatus for a workpiece, and more particularly, to a method of cutting composite material and a cutting apparatus for cutting composite material.
2. Related Art
In order to divide a semiconductor wafer into chips, a cutting apparatus such as a dicing apparatus is known in which the semiconductor wafer is cut by a cutting blade attached to a hub base. In a cutting apparatus of this type, restraining a rise in temperature at the point of contact between the blade and the workpiece as well as reducing the incidence of chipping without increasing cutting resistance are continuing technical problems. Consequently, cutting using ultrasonic vibration is being studied as one means of solving this problem. “Ultrasonic” means the range of sound above the frequencies audible to humans (approximately 20 kHz and above).
One example of a cutting method employing this type of ultrasonic vibration is JP-A-2002-336775, in which a method of cutting by ultrasonically vibrating a cutting blade is described. With this method, the cutting blade is bent in the direction of the thickness of the cutting blade (in the direction of the axis of rotation) and ultrasonically vibrated. A problem with this method is that, because a force acts to widen the cutting groove formed in the semiconductor wafer by the ultrasonically vibrated cutting blade, cutting resistance inevitably increases, leading to chipping of the devices formed from the wafer.
One method of solving this problem is disclosed in, for example, JP-A-2000-210928, which describes a method of cutting a workpiece by ultrasonically vibrating the cutting blade in the direction of the diameter of the blade. With this method, the ultrasonic vibration is transmitted in the direction of the axis of rotation of a spindle on which the cutting blade is mounted, the direction of vibration is changed by a vibration transmission direction converter mounted with the cutting blade, and the cutting blade is vibrated in the direction of the diameter of the blade.
Compared to the usual cutting process using a cutting blade that is not ultrasonically vibrated, cutting a workpiece with a cutting blade that is ultrasonically vibrated in the direction of the diameter of the blade as described above has the following advantages: (1) since the cutting resistance can be decreased, chipping can be restrained; (2) since cutting water can be supplied easily to the point of contact between the blade and the workpiece, the rise in temperature at the point of contact can be restrained and warping due to heat does not occur easily; (3) any contamination attached to the cutting blade is shaken off by the vibration, and therefore the cutting blade is uncontaminated; and (4) the load on the cutting blade is lightened, extending its life. In particular, this method can be expected to be able to cut cleanly such hard materials as quartz, glass and the like that are difficult to cut by dicing using conventional cutting blades.
However, it became cl ear that cutting a workpiece using a cutting blade that is vibrated in the direction of the diameter of the blade by ultrasonic vibration has the opposite of the effect intended, in that, depending on the type of material, the incidence of chipping increases compared to cutting with the usual cutting blade.
For example, an image sensing device such as a CCD or a C-MOS is a structure that uses an adhesive agent to bond together glass and silicon on the front surface of which circuits are formed.
With cutting using the usual cutting blade, because the blade cannot cut the glass portion, or the blade can cut the glass portion but the cutting speed with which the blade cuts the glass portion is slow or the quality of the cut diminishes and so forth, it has been difficult to cut the glass. Consequently, it was thought that, if the workpiece were cut with a cutting blade that is vibrated in the direction of the diameter of the blade by ultrasonic vibration, the glass portion could be cut cleanly.
However, when the above-described image sensing device such as a CCD or a C-MOS is cut with an ultrasonically vibrated cutting blade, although the glass portion is cut cleanly, the incidence of chipping increases by 10% over the conventional method.
Investigation of the relevant factors leading to such a high incidence of chipping indicates that, when cutting workpiece consisting of crystal material such as silicon with a cutting blade that is vibrated in the direction of the diameter of the blade using ultrasonic vibration, chipping occurs due to the cleavage of the crystal material.